Light-irradiation heat treatment method and heat treatment apparatus

ABSTRACT

Over a front surface of a silicon semiconductor wafer is deposited a high dielectric constant film with a silicon oxide film, serving as an interface layer, provided between the semiconductor wafer and the high dielectric constant film. After a chamber houses the semiconductor wafer, a chamber&#39;s pressure is reduced to be lower than atmospheric pressure. Subsequently, a gaseous mixture of ammonia and nitrogen gas is supplied into the chamber to return the pressure to ordinary pressure, and the front surface is irradiated with a flash light, thereby performing post deposition annealing (PDA) on the high dielectric constant film. Since the pressure is reduced once to be lower than atmospheric pressure and then returned to ordinary pressure, a chamber&#39;s oxygen concentration is lowered remarkably during the PDA. This restricts an increase in thickness of the silicon oxide film underlying the high dielectric constant film by oxygen taken in during the PDA.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a heat treatment method and a heattreatment apparatus for irradiating a thin-plate-shaped precisionelectronic substrate (hereinafter referred to simply as a “substrate”),such as a semiconductor wafer including a high dielectric constant filmor including a metal gate formed on a high dielectric constant film,with a flash of light to heat the substrate.

Description of the Background Art

In the process of manufacturing a semiconductor device, attention hasbeen paid to flash lamp annealing (FLA) that heats a semiconductor waferin an extremely short time. The flash lamp annealing is a heat treatmenttechnique in which xenon flash lamps (the term “flash lamp” as usedhereinafter refers to a “xenon flash lamp”) are used to irradiate asurface of a semiconductor wafer with a flash of light, thereby raisingthe temperature of only the surface of the semiconductor wafer in anextremely short time (several milliseconds or less).

The xenon flash lamps have a spectral distribution of radiation rangingfrom ultraviolet to near-infrared regions. The wavelength of the lightemitted from the xenon flash lamps is shorter than that of the lightemitted from conventional halogen lamps, and substantially coincideswith a fundamental absorption band of a silicon semiconductor wafer.Thus, when a semiconductor wafer is irradiated with a flash of lightemitted from the xenon flash lamps, the temperature of the semiconductorwafer can be raised rapidly, with only a small amount of lighttransmitted through the semiconductor wafer. Also, it has turned outthat flash irradiation, that is, the irradiation of a semiconductorwafer with a flash of light in an extremely short time of severalmilliseconds or less allows a selective temperature rise only near thesurface of the semiconductor wafer.

Such flash lamp annealing is used for processes that require heating inan extremely short time, for example, typically for the activation ofimpurities implanted in a semiconductor wafer. The irradiation of asurface of a semiconductor wafer implanted with impurities by an ionimplantation process with a flash of light from flash lamps allows atemperature rise to an activation temperature only in the surface of thesemiconductor wafer in an extremely short time, thereby enabling onlythe activation of impurities without deep diffusion of the impurities.

It is considered that a high dielectric gate film (high-k film)including a material (high dielectric constant material) having adielectric constant higher than that of silicon dioxide (SiO₂) is usedas a gate insulating film of a field-effect transistor (FET) underdevelopment. The high dielectric constant film is under development as anew stack structure together with a metal gate including a gateelectrode of metal to solve a problem of an increased leakage currentassociated with a thinner gate insulating film. It is also consideredthat flash lamp annealing is applied to the heat treatment of asemiconductor wafer having a new stack structure including such a highdielectric constant film.

The high dielectric constant film is formed by depositing a highdielectric constant material on a silicon base material by a techniquesuch as metal organic chemical vapor deposition (MOCVD). Although thehigh dielectric constant film has a dielectric constant higher than thatof a conventional silicon oxide film, the high dielectric constant filmimmediately after deposition has low crystallinity and involves manydefects such as point defects. The deposited high dielectric constantfilm thus needs to be annealed at high temperature. For example, US2013/0078786 proposes that the surface of a semiconductor waferincluding a high dielectric constant film formed thereover be irradiatedwith a flash of light for a heat treatment in a short time.

Unfortunately, it has turned out that a high dielectric constant cannotbe obtained due to an increased thickness of the silicon oxide filmunderlying the high dielectric constant film by merely irradiating asemiconductor wafer including the high dielectric constant film formedthereover with a flash of light as disclosed in US 2013/0078786. Anincrease in thickness of a silicon oxide film results from a heattreatment performed in the presence of oxygen. Examples of the oxygenthat causes an increase in film thickness include residual oxygen in achamber, oxygen adsorbed on the surface of the semiconductor wafer(typically adsorbed in the form of water), and oxygen present as a solidsolution in a high dielectric constant film itself. In particular, theoxygen remaining in the chamber during the flash heating treatment islargely responsible for the increase in thickness of a silicon oxidefilm. In general, semiconductor wafers are transported into and out of achamber at ordinary pressure in a flash lamp annealer, and accordingly,oxygen in the atmosphere flowing into the chamber during the transportremains in the chamber to increase the concentration of oxygen.

When a flash heating treatment is performed on a semiconductor waferincluding a metal gate deposited on a high dielectric constant film,oxygen may diffuse through the metal gate and the high dielectricconstant film to increase the thickness of the silicon oxide filmunderlying the high dielectric constant film and to oxide the metal gateitself.

SUMMARY OF THE INVENTION

The present invention is directed to a method of irradiating a substrateincluding a high dielectric constant film deposited thereover with aflash of light to heat the substrate.

According to one aspect of the present invention, the method includes(a) transporting a substrate including a high dielectric constant filmdeposited thereover into a chamber, (b) reducing a pressure in thechamber to a first pressure lower than atmospheric pressure, (c)returning the pressure in the chamber from the first pressure to asecond pressure higher than the first pressure, and (d) irradiating afront surface of the substrate with a flash of light from a flash lampwhile maintaining the pressure in the chamber at the second pressure.

The concentration of oxygen in the chamber during the irradiation with aflash of light can be reduced, thus restricting an increase in thicknessof a silicon oxide film underlying the high dielectric constant film.

Preferably, the first pressure is not greater than one-hundredth of thesecond pressure.

The influence of remaining air on a reactive gas is reduced.

Preferably, the method further includes (e) before the step (d), raisinga temperature of the substrate to a predetermined preheatingtemperature. In the step (e), a supply of the reactive gas into thechamber is performed in the step (e), and the supply of the reactive gasinto the chamber is stopped after the step (d).

The high dielectric constant film is nitrided to some extent, andhydrogen that has entered the high dielectric constant film is desorbed.

Preferably, the second pressure is higher than the first pressure andlower than atmospheric pressure.

The mean free path in irradiation with a flash of light is increased,resulting in a uniform reaction of the high dielectric constant film tothe heat treatment. Also, a less time is required for the pressurereturn, thus improving a throughput.

Preferably, the second pressure is higher than atmospheric pressure.

The reaction of the high dielectric constant film to the heat treatmentproceeds even when the treatment temperature during the irradiation witha flash of light is reduced.

Preferably, an exhaust flow rate from the chamber is increased with timein the step (b).

Particles caused by the exhaustion of the gas from the chamber areprevented from swirling up.

Preferably, a supply flow rate into the chamber is increased with timein the step (c).

Particles caused by the supply of the gas into the chamber are preventedfrom swirling up. Preferably, after the step (d), when a gas in thechamber is discharged and then an inert gas is supplied into the chamberso that the pressure in the chamber returns to atmospheric pressure, theinert gas is caused to flow at a flow rate ranging from 50 to 100 litersper minute in the chamber.

Particles caused during the irradiation with a flash of light are sweptaway out of the chamber.

The present invention is also directed to a heat treatment apparatus forirradiating a substrate including a high dielectric constant filmdeposited thereover with a flash of light to heat the substrate.

According to one aspect of the present invention, a heat treatmentapparatus includes a chamber that houses the substrate, a flash lampthat irradiates the substrate housed in the chamber with a flash oflight, an exhaust part that exhausts an atmosphere in the chamber, a gassupply part that supplies a predetermined treatment gas to the chamber,and a controller that controls the exhaust part and the gas supply partso that a front surface of the substrate is irradiated with a flash oflight from the flash lamp while a pressure in the chamber is reduced toa first pressure lower than atmospheric pressure and then returned to asecond pressure higher than the first pressure.

The concentration of oxygen in the chamber is reduced during theirradiation with a flash of light, thus restricting an increase inthickness of a silicon oxide film underlying the high dielectricconstant film.

Preferably, the first pressure is not greater than one-hundredth of thesecond pressure.

The influence of remaining air on a reactive gas is reduced.

Preferably, the heat treatment apparatus further includes a preheatingpart that raises a temperature of the substrate to a predeterminedpreheating temperature before the substrate is irradiated with the flashof light. The controller controls the exhaust part and the gas supplypart so that the reactive gas is supplied into the chamber when thepreheating part preheats the substrate and that the supply of thereactive gas into the chamber is stopped after the substrate isirradiated with the flash of light.

The high dielectric constant film is nitrided to some extent, andhydrogen that has entered the high dielectric constant film is desorbed.

Preferably, the second pressure is higher than the first pressure andlower than atmospheric pressure.

The mean free path in irradiation with a flash of light is increased,resulting in a uniform reaction of the high dielectric constant film tothe heat treatment. Also, a less time is required for the pressurereturn, thus improving a throughput.

Preferably, the second pressure is higher than atmospheric pressure.

The reaction of the high dielectric constant film to the heat treatmentproceeds even when the treatment temperature during the irradiation witha flash of light is reduced.

Preferably, the controller controls the gas exhaust part so that anexhaust flow rate from the chamber increases with time when the pressurein the chamber is reduced to the first pressure.

Particles caused by the exhaustion of the gas from the chamber areprevented from swirling up.

Preferably, the controller controls the gas supply part so that a supplyflow rate to the chamber increases with time when the pressure in thechamber is returned from the first pressure to the second pressure.

Particles caused by the supply of the gas into the chamber are preventedfrom swirling up.

Preferably, the controller controls the exhaust part and the gas supplypart so that, after the irradiation with the flash of light, when a gasin the chamber is discharged and then an inert gas is supplied into thechamber to return the pressure in the chamber to atmospheric pressure,the inert gas is caused to flow in the chamber at a flow rate rangingfrom 50 to 100 liters per minute.

Particles caused during the irradiation with a flash of light are sweptaway out of the chamber.

The present invention therefore has an object to restrict an increase inthickness of a silicon oxide film underlying a high dielectric constantfilm.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a configuration of aheat treatment apparatus according to the present invention;

FIG. 2 is a perspective view of the entire external appearance of aholder;

FIG. 3 is a plan view of the holder as seen from above;

FIG. 4 is a side view of the holder as seen from one side;

FIG. 5 is a plan view of a transfer mechanism;

FIG. 6 is a side view of the transfer mechanism;

FIG. 7 is a plan view of an arrangement of halogen lamps;

FIG. 8 is a view of a configuration of an exhaust part;

FIG. 9 is a view of a stack structure in which a high dielectricconstant film is deposited over a semiconductor wafer;

FIG. 10 is a graph showing changes in pressure in a chamber according toa first preferred embodiment of the present invention;

FIG. 11 is a graph showing changes in pressure in the chamber accordingto a second preferred embodiment of the present invention; and

FIG. 12 is a graph showing changes in pressure in the chamber accordingto a third preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the drawings.

First Preferred Embodiment

FIG. 1 is a longitudinal cross-sectional view of a configuration of aheat treatment apparatus 1 according to the present invention. The heattreatment apparatus 1 according to the present preferred embodiment is aflash lamp annealer for irradiating a disk-shaped semiconductor wafer Wserving as a substrate with a flash of light to heat the semiconductorwafer W. The diameter size of the semiconductor wafer W to be treated isnot particularly limited, which is, for example, 300 or 450 mm. Thewafer W before being transported into the heat treatment apparatus 1 hasa high dielectric constant film deposited thereover, and the heattreatment apparatus 1 performs post deposition annealing (PDA) on thehigh dielectric constant film through a heating treatment. For easyunderstanding, the dimensions and the numbers of respective constituentelements may be exaggerated or simplified as necessary in FIG. 1 andsubsequent drawings.

The heat treatment apparatus 1 includes a chamber 6 that houses thesemiconductor wafer W, a flash heating part 5 with a plurality ofbuilt-in flash lamps FL, and a halogen heating part 4 with a pluralityof built-in halogen lamps HL. The flash heating part 5 is located abovethe chamber 6, and the halogen heating part 4 is located below thechamber 6. The heat treatment apparatus 1 further includes, within thechamber 6, a holding part 7 that holds the semiconductor wafer W in ahorizontal position and a transfer mechanism 10 that transfers thesemiconductor wafer W between the holding part 7 and the outside of theheat treatment apparatus 1. The heat treatment apparatus 1 furtherincludes a controller 3 that controls operating mechanisms located inthe halogen heating part 4, the flash heating part 5, and the chamber 6for heat treatment of the semiconductor wafer W.

The chamber 6 is configured such that chamber windows made of quartz aremounted to the top and bottom of a tubular chamber side portion 61. Thechamber side portion 61 has a substantially tubular shape having an opentop and an open bottom. An upper chamber window 63 is mounted to blockthe top opening of the chamber side portion 61, and a lower chamberwindow 64 is mounted to block the bottom opening thereof. The upperchamber window 63 forming the ceiling of the chamber 6 is a disk-shapedmember made of quartz and serves as a quartz window that transmits aflash of light emitted from the flash heating part 5 therethrough intothe chamber 6. The lower chamber window 64 forming the floor of thechamber 6 is also a disk-shaped member made of quartz and serves as aquartz window that transmits light emitted from the halogen heating part4 therethrough into the chamber 6. The upper chamber window 63 and thelower chamber window 64 have a thickness of, for example, approximately28 mm.

A reflection ring 68 is mounted to an upper portion of the inner wallsurface of the chamber side portion 61, and a reflection ring 69 ismounted to a lower portion thereof. The reflection rings 68 and 69 areeach in the form of an annular ring. The reflection ring 68 on the topis mounted by being inserted downwardly from the top of the chamber sideportion 61. The reflection ring 69 on the bottom, on the other hand, ismounted by being inserted upwardly from the bottom of the chamber sideportion 61 and fastened with screws (not shown). In other words, thereflection rings 68 and 69 are each removably mounted to the chamberside portion 61. An interior space of the chamber 6, or, a spacesurrounded by the upper chamber window 63, the lower chamber window 64,the chamber side portion 61, and the reflection rings 68 and 69, isdefined as a heat treatment space 65.

A recessed portion 62 is defined in the inner wall surface of thechamber 6 by mounting the reflection rings 68 and 69 to the chamber sideportion 61. Specifically, the recessed portion 62 is defined which issurrounded by a middle portion of the inner wall surface of the chamberside portion 61 where the reflective rings 68 and 69 are not mounted, alower end surface of the reflection ring 68, and an upper end surface ofthe reflection ring 69. The recessed portion 62 is horizontally formedin an annular shape in the inner wall surface of the chamber 6 andsurrounds the holding part 7 that holds the semiconductor wafer W.

The chamber side portion 61 and the reflection rings 68 and 69 are madeof metal material (e.g., stainless steel) with high strength and highheat resistance. The inner peripheral surfaces of the reflection rings68 and 69 are provided as mirror surfaces by electrolytic nickelplating.

The chamber side portion 61 is provided with a transport opening(throat) 66 for the transport of a semiconductor wafer W therethroughinto and out of the chamber 6.

The transport opening 66 is openable and closable by a gate valve 185.The transport opening 66 is connected in communication with an outerperipheral surface of the recessed portion 62. Thus, when the transportopening 66 is opened by the gate valve 185, a semiconductor wafer W isallowed to be transported through the transport opening 66 and therecessed portion 62 into and out of the heat treatment space 65. Whenthe transport opening 66 is closed by the gate valve 185, the heattreatment space 65 in the chamber 6 is an enclosed space.

The upper portion of the inner wall of the chamber 6 has a gas supplyport 81 through which a treatment gas (in the present preferredembodiment, nitrogen gas (N₂) and ammonia (NH₃)) is supplied into theheat treatment space 65. The gas supply port 81 is located at a positionabove the recessed portion 62 and may be located in the reflection ring68. The gas supply port 81 is communicatively connected to a gas supplypipe 83 via a buffer space 82 that is formed in an annular shape insidethe side wall of the chamber 6. The gas supply pipe 83 is connected to agas supply source 85. The gas supply source 85 supplies the gas supplypipe 83 with a nitrogen gas or a gaseous mixture of ammonia and nitrogengas as a treatment gas under the control of the controller 3. Also, avalve 84 and a flow regulating valve 90 are interposed in the path ofthe gas supply pipe 83. When the valve 84 is opened, a treatment gas issupplied from the gas supply source 85 into the buffer space 82. Theflow rate of the treatment gas flowing through the gas supply pipe 83 tothe buffer space 82 is regulated by the flow regulating valve 90. Theflow rate of the treatment gas determined by the flow regulating valve90 is variable through the control of the controller 3. The treatmentgas flowing in the buffer space 82 flows in a spreading manner withinthe buffer space 82 that is lower in fluid resistance than the gassupply opening 81, and is supplied through the gas supply opening 81into the heat treatment space 65. It should be noted that the treatmentgas is not limited to nitrogen gas and ammonia, but may be inert gasessuch as argon (Ar) and helium (He), and reactive gases such oxygen (O₂),hydrogen (H₂), chlorine (Cl₂), hydrogen chloride (HCl), ozone (O₃),carbon monoxide (NO), nitrous oxide (N₂O), and nitrogen dioxide (NO₂).

The lower portion of the inner wall of the chamber 6 has a gas exhaustport 86 through which the gas in the heat treatment space 65 isexhausted. The gas exhaust port 86 is located at a position below therecessed portion 62 and may be located in the reflection ring 69. Thegas exhaust port 86 is communicatively connected to a gas exhaust pipe88 via a buffer space 87 that is formed in an annular shape inside theside wall of the chamber 6. The gas exhaust pipe 88 is connected to anexhaust part 190. Also, a valve 89 is interposed in the path of the gasexhaust pipe 88. When the valve 89 is opened, the gas in the heattreatment space 65 is exhausted from the gas exhaust port 86 through thebuffer space 87 into the gas exhaust pipe 88. Alternatively, a pluralityof gas supply ports 81 and a plurality of gas exhaust ports 86 may beprovided along the circumference of the chamber 6, or the gas supplyport 81 and the gas exhaust port 86 may be slit-shaped.

FIG. 8 is a view of a configuration of the exhaust part 190. The exhaustpart 190 includes an exhaust pump 191, a flow regulating valve 196,three bypass lines 197, 198, and 199, and three exhaust valves 192, 193,and 194. The gas exhaust pipe 88 guiding the gas exhausted from thechamber 6 is connected through the three bypass lines 197, 198, and 199to the exhaust pump 191. The three bypass lines 197, 198, and 199 areprovided in parallel with each other. The three bypass lines 197, 198,and 199 are different in pipe diameter from each other. The bypass line197 has the smallest diameter, and the bypass line 199 has the largestdiameter. The bypass line 198 has a diameter intermediate between thediameters of the bypass lines 197 and 199. Thus, the flow rate of thegas that can pass through the bypass line increases in the order of thebypass lines 197, 198, and 199.

The three exhaust valves 192, 193, and 194 are provided respectively inthe three bypass lines 197, 198, and 199. Specifically, the exhaustvalve 192 is interposed in the bypass line 197, the exhaust valve 193 isinterposed in the bypass line 198, and the exhaust valve 194 isinterposed in the bypass line 199. When the three exhaust valves 192,193, and 194 are opened while the exhaust pump 191 is operated, the gasexhausted from the chamber 6 and guided by the gas exhaust pipe 88passes through the corresponding bypass lines 197, 198, and 199 and isthen sucked by the exhaust pump 191.

The three bypass lines 197, 198, and 199, which have different pipediameters, are different in exhaust capability from each other. Theexhaust capability increases as the pipe diameter increases. The exhaustcapability increases in the order of the bypass lines 197, 198, and 199.Thus, the exhaust flow rate from the chamber 6 can be controlled byopening or closing any of the three exhaust valves 192, 193, and 194.Any one of the three exhaust valves 192, 193, and 194 may be opened.Alternatively, two or all of the three exhaust valves 192, 193, and 194may be opened. For example, when the exhaust valves 193 and 194 areclosed and only the exhaust valve 192 is opened, the gas is exhausted atthe lowest exhaust flow rate. When all the three exhaust valves 192,193, and 194 are opened, the gas is exhausted at the highest exhaustflow rate.

The flow regulating valve 196 is interposed between the exhaust pump 191and the joint portion of the three bypass lines 197, 198, and 199. Theexhaust flow rate in the gas exhaust pipe 88 is also regulatable by theflow regulating valve 196. The exhaust flow rate determined by the flowregulating valve 196 is variable through the control of the controller3. While the three bypass lines 197, 198, and 199 constitute a mechanismthat regulates the exhaust flow rate in a discontinuous and multi-stepmanner, the flow regulating valve 196 is a mechanism that regulates theexhaust flow rate in a continuous and stepless manner.

The gas supply pipe 83, the gas exhaust pipe 88, and the three bypasslines 197, 198, and 199 are made of stainless steel with high strengthand high resistance to corrosion. A pressure gauge 180 for measuring thepressure in the heat treatment space 65 is provided in the chamber 6.The pressure gauge 180 preferably has a measurement range ofapproximately 5 Pa to 0.2 MPa.

FIG. 2 is a perspective view of the entire external appearance of aholder 7. FIG. 3 is a plan view of the holder 7 as seen from the above.FIG. 4 is a side view of the holder 7 as seen from one side. The holder7 includes a base ring 71, coupling portions 72, and a susceptor 74. Thebase ring 71, the coupling portions 72, and the susceptor 74 are allmade of quartz. In other words, the whole of the holder 7 is made ofquartz.

The base ring 71 is a quartz member in the form of an annular ring. Thebase ring 71 is supported by the wall surface of the chamber 6 by beingplaced on the bottom surface of the recessed portion 62 (see FIG. 1).The plurality of (in the present preferred embodiment, four) couplingportions 72 are mounted upright on the upper surface of the base ring 71in the form of an annular ring and arranged in a circumferentialdirection of the base ring 71. The coupling portions 72 are also quartzmembers, and are rigidly secured to the base ring 71 by welding. Thebase ring 71 may have an arc shape that is an annular shape with amissing part.

The susceptor 74 having a planar shape is supported by the four couplingportions 72 provided on the base ring 71. The susceptor 74 is asubstantially circular planar member made of quartz. The diameter of thesusceptor 74 is greater than that of a semiconductor wafer W. In otherwords, the susceptor 74 has a size, as seen in a plan view, greater thanthat of the semiconductor wafer W. A plurality of (in the presentpreferred embodiment, five) guide pins 76 are mounted upright on theupper surface of the susceptor 74. The five guide pins 76 are locatedalong the circumference of a circle concentric with the outercircumference of the susceptor 74. The diameter of a circle on which thefive guide pins 76 are located is slightly greater than the diameter ofthe semiconductor wafer W. The guide pins 76 are also made of quartz.The guide pins 76 may be machined from a quartz ingot integrally withthe susceptor 74. Alternatively, the guide pins 76 separately machinedmay be attached to the susceptor 74 by, for example, welding.

The four coupling portions 72 provided upright on the base ring 71 andthe lower surface of a peripheral portion of the susceptor 74 arerigidly secured to each other by welding. In other words, the susceptor74 and the base ring 71 are fixedly coupled to each other with thecoupling portions 72, and the holder 7 is an integrally formed membermade of quartz. The base ring 71 of such a holder 7 is supported by thewall surface of the chamber 6, whereby the holder 7 is mounted to thechamber 6. With the holder 7 mounted to the chamber 6, the susceptor 74of a substantially disk-shaped configuration is held in the horizontalposition (the position in which the normal to the susceptor 74 coincideswith a vertical direction). A semiconductor wafer W transported into thechamber 6 is placed and held in the horizontal position on the susceptor74 of the holder 7 mounted to the chamber 6. The semiconductor wafer Wis placed inside the circle defined by the five guide pins 76. Thisprevents a positional deviation of the semiconductor wafer W in thehorizontal direction. The number of guide pins 76 is not limited to fiveand may be determined so as to prevent a positional deviation of thesemiconductor wafer W.

As shown in FIGS. 2 and 3, an opening 78 and a cut-out portion 77 areprovided in the susceptor 74 that vertically penetrate the susceptor 74.The cut-out portion 77 is provided to allow a distal end portion of aprobe of a contact-type thermometer 130 including a thermocouple to passtherethrough. The opening 78 is provided for a radiation thermometer 120to receive radiation (infrared radiation) emitted from the lower surfaceof the semiconductor wafer W held by the susceptor 74. The susceptor 74further has four through holes 79 through which lift pins 12 of thetransfer mechanism 10, which will be described below, pass to transferthe semiconductor wafer W.

FIG. 5 is a plan view of the transfer mechanism 10. FIG. 6 is a sideview of the transfer mechanism 10. The transfer mechanism 10 includes apair of transfer arms 11. The transfer arms 11 are of an arcuateconfiguration extending substantially along the annular recessed portion62. Each of the transfer arms 11 includes the pair of lift pins 12mounted upright thereon. The transfer arms 11 are pivotable by ahorizontal movement mechanism 13. The horizontal movement mechanism 13moves the pair of transfer arms 11 horizontally between a transferoperation position (a position indicated by solid lines in FIG. 5) inwhich a semiconductor wafer W is transferred to and from the holder 7and a retracted position (a position indicated by dashed double-dottedlines in FIG. 5) in which the transfer arms 11 do not overlap thesemiconductor wafer W held by the holder 7 as seen in a plan view. Thehorizontal movement mechanism 13 may be a mechanism for separatelypivoting the transfer arms 11 by individual motors or a mechanism forpivoting the pair of transfer arms 11 in conjunction with each other bya single motor using a link mechanism.

The pair of transfer arms 11 are movable upward and downward togetherwith the horizontal movement mechanism 13 by an elevating mechanism 14.When the elevating mechanism 14 moves up the pair of transfer arms 11 intheir transfer operation position, the four lift pins 12 in total passthrough the respective four through holes 79 (see FIGS. 2 and 3) boredin the susceptor 74, so that the upper ends of the lift pins 12 protrudefrom the upper surface of the susceptor 74. On the other hand, when theelevating mechanism 14 moves down the pair of transfer arms 11 in theirtransfer operation position to take the lift pins 12 out of therespective through holes 79 and the horizontal movement mechanism 13moves the pair of transfer arms 11 so as to open the transfer arms 11,the transfer arms 11 move to their retracted position. The retractedposition of the pair of transfer arms 11 is directly above the base ring71 of the holder 7. The base ring 71 is placed on the bottom surface ofthe recessed portion 62, and thus, the retracted position of thetransfer arms 11 is inside the recessed portion 62.

Referring back to FIG. 1, the flash heating part 5 provided over thechamber 6 includes an enclosure 51, a light source provided inside theenclosure 51 and including the plurality of (in the present preferredembodiment, 30) xenon flash lamps FL, and a reflector 52 provided insidethe enclosure 51 so as to cover the light source from above. The flashheating part 5 further includes a lamp light irradiation window 53mounted to the bottom of the enclosure 51. The lamp light irradiationwindow 53 forming the floor of the flash heating part 5 is aplate-shaped quartz window made of quartz. The flash heating part 5 isprovided over the chamber 6, whereby the lamp light irradiation window53 is opposed to the upper chamber window 63. The flash lamps FL emit aflash of light from over the chamber 6 through the lamp lightirradiation window 53 and the upper chamber window 63 toward the heattreatment space 65.

The flash lamps FL, each of which is a rod-shaped lamp having anelongated cylindrical shape, are arranged in a plane so that thelongitudinal directions of the respective flash lamps FL are parallelwith each other along the main surface of a semiconductor wafer W heldby the holder 7 (i.e., in a horizontal direction). Thus, a plane definedby the arrangement of the flash lamps FL is also a horizontal plane.

Each of the xenon flash lamps FL includes a rod-shaped glass tube(discharge tube) and a trigger electrode. The glass tube contains axenon gas sealed therein and has positive and negative electrodesprovided on opposite ends thereof and connected to a capacitor. Thetrigger electrode is attached to the outer peripheral surface of theglass tube. The xenon gas is electrically insulative, and thus, nocurrent flows in the glass tube in a normal state even when electricalcharge is stored in the capacitor. However, if a high voltage is appliedto the trigger electrode to cause an electrical breakdown, theelectricity stored in the capacitor flows momentarily in the glass tube,and xenon atoms or molecules are excited at this time to cause lightemission. Such a xenon flash lamp FL has the property of being capableof emitting extremely intense light compared with a light source thatstays lit continuously, such as a halogen lamp HL, because theelectrostatic energy previously stored in the capacitor is convertedinto an ultrashort light pulse ranging from 0.1 to 100 milliseconds.Thus, the flash lamps FL are pulsed light emitting lamps that emit lightinstantaneously for an extremely short time period of less than onesecond. The light emission time of the flash lamps FL is adjustable inaccordance with the coil constant of a lamp light source that suppliespower to the flash lamps FL.

The reflector 52 is provided over the plurality of flash lamps FL so asto cover all the flash lamps FL. A fundamental function of the reflector52 is to reflect flashes of light emitted from the plurality of flashlamps FL toward the heat treatment space 65.

The reflector 52 is a plate made of aluminum alloy. A surface of thereflector 52 (a surface that faces the flash lamps FL) is roughened byblasting.

The halogen heating part 4 provided below the chamber 6 includes aplurality of (in the present preferred embodiment, 40) built-in halogenlamps HL inside an enclosure 41. The halogen heating part 4 is a lightirradiator that emits light from under the chamber 6 through the lowerchamber window 64 toward the heat treatment space 65 to heat thesemiconductor wafer W by means of the halogen lamps HL.

FIG. 7 is a plan view of an arrangement of the plurality of halogenlamps HL. The 40 halogen lamps HL are arranged in two tiers, or, upperand lower tiers. That is, 20 halogen lamps HL are arranged in the uppertier closer to the holder 7, and 20 halogen lamps HL are arranged in thelower tier farther from the holder 7 than the upper tier. Each of thehalogen lamps HL is a rod-shaped lamp having an elongated cylindricalshape. The 20 halogen lamps HL in the upper tier and the 20 halogenlamps HL in the lower tier are arranged so that the longitudinaldirections thereof are parallel with each other along a main surface ofa semiconductor wafer W held by the holder 7 (i.e., in a horizontaldirection). Thus, a plane defined by the arrangement of the halogenlamps HL in each of the upper and lower tiers is also a horizontalplane.

As shown in FIG. 7, the halogen lamps HL in each of the upper and lowertiers are disposed at a higher density in a region opposed to theperipheral portion of the semiconductor wafer W held by the holder 7than in a region opposed to the central portion thereof. In other words,the halogen lamps HL in each of the upper and lower tiers are arrangedat shorter intervals in the peripheral portion of the lamp arrangementthan in the central portion thereof. This allows a greater amount oflight to impinge upon the peripheral portion of the semiconductor waferW in which a temperature drop tends to occur when the semiconductorwafer W is heated by the irradiation thereof with light from the halogenheating part 4.

The group of halogen lamps HL in the upper tier and the group of halogenlamps HL in the lower tier are arranged to intersect each other in alattice pattern. In other words, the 40 halogen lamps HL in total aredisposed so that the longitudinal direction of the 20 halogen lamps HLarranged in the upper tier and the longitudinal direction of the 20halogen lamps HL arranged in the lower tier are orthogonal to eachother.

Each of the halogen lamps HL is a filament-type light source that passescurrent through a filament disposed in a glass tube to make the filamentincandescent, thereby emitting light. A gas prepared by introducing atrace amount of halogen element (e.g., iodine or bromine) into an inertgas such as nitrogen or argon is sealed in the glass tube. Theintroduction of the halogen element allows the temperature of thefilament to be set at a high temperature while restricting a break inthe filament. Thus, the halogen lamps HL have the properties of having alonger life than typical incandescent lamps and being capable ofcontinuously emitting intense light. Thus, the halogen lamps HL arecontinuously lighting lamps that emit light continuously for at leastone second or more. In addition, the halogen lamps HL, which arerod-shaped lamps, have a longer life. The arrangement of the halogenlamps HL in a horizontal direction provides good efficiency of radiationtoward the semiconductor wafer W provided over the halogen lamps HL.

A reflector 43 is provided also inside the enclosure 41 of the halogenheating part 4, under the halogen lamps HL arranged in two tiers (FIG.1). The reflector 43 reflects the light emitted from the halogen lampsHL toward the heat treatment space 65.

The controller 3 controls the aforementioned various operatingmechanisms provided in the heat treatment apparatus 1. The controller 3is similar in hardware configuration to a typical computer.Specifically, the controller 3 includes a CPU that is a circuit forperforming various computation processes, a ROM or read-only memory forstoring a basic program, a RAM or readable/writable memory for storingvarious pieces of information, and a magnetic disk for storing controlsoftware, data, and the like. The CPU of the controller 3 executes apredetermined processing program, whereby the processes in the heattreatment apparatus 1 proceed. Also, the controller 3 controls the valve84, the valve 89, the flow regulating valve 90, the flow regulatingvalve 196, the exhaust pump 191, and the three exhaust valves 192, 193,and 194 to adjust the pressure in the heat treatment space 65 of thechamber 6, a gas supply flow rate to the chamber 6, and an exhaust flowrate from the chamber 6.

The heat treatment apparatus 1 further includes, in addition to theaforementioned components, various cooling structures to prevent anexcessive temperature rise in the halogen heating part 4, the flashheating part 5, and the chamber 6 because of the heat energy generatedfrom the halogen lamps HL and the flash lamps FL during the heattreatment of a semiconductor wafer W. For example, a water cooling tube(not shown) is provided in the walls of the chamber 6. Also, the halogenheating part 4 and the flash heating part 5 have an air coolingstructure for forming a gas flow therein to exhaust heat. Air issupplied to a gap between the upper chamber window 63 and the lamp lightirradiation window 53 to cool the flash heating part 5 and the upperchamber window 63.

A procedure for treatment of a semiconductor wafer W in the heattreatment apparatus 1 will now be described. A semiconductor wafer W tobe treated herein is a semiconductor substrate including a highdielectric constant film formed thereover as a gate insulating film. Theheat treatment apparatus 1 irradiates a semiconductor wafer W with aflash of light in an ammonia atmosphere to perform post depositionannealing (PDA) on the semiconductor wafer W, thereby eliminatingdefects in the high dielectric constant film and also nitriding the highdielectric constant film.

FIG. 9 is a view of a stack structure in which a high dielectricconstant film is deposited over a semiconductor wafer W. A silicon oxidefilm (SiO₂) 102 is formed on a base material 101 of silicon of thesemiconductor wafer W. The silicon oxide film 102 is a layer required asan interfacial film between the base material 101 of silicon and a highdielectric constant film 103. The thickness of the silicon oxide film102 is extremely small and is, for example, approximately 1 nm. Variousknown methods such as a thermal oxidation method may be employed as atechnique for forming the silicon oxide film 102.

The high dielectric constant film 103 is formed on the silicon oxidefilm 102 as a gate insulating film. The material for the high dielectricconstant film 103 may be a high dielectric constant material such asHfO₂, ZrO₂, Al₂O₃, or La₂O₃ (in the present preferred embodiment, HfO₂).The high dielectric constant film 103 is formed by, for example,depositing such a high dielectric constant material on the silicon oxidefilm 102 by atomic layer deposition (ALD). Although the high dielectricconstant film 103 deposited on the silicon oxide film 102 has athickness of several nanometers, the equivalent oxide thickness (EOT) ofthe high dielectric constant film 103 is approximately 1 nm. Thetechnique of forming the high dielectric constant film 103 is notlimited to the ALD, and for example, known techniques such as metalorganic chemical vapor deposition (MOCVD) may be employed. If anytechnique is employed, many defects such as point defects are present inthe high dielectric constant film 103 that has not undergone a specificprocess after deposition. In the structure of FIG. 9, side walls 104 ofSiN are formed at both sides of the high dielectric constant film 103,which are formed before the formation of the high dielectric constantfilm 103 in, for example, the gate-last process. After the heattreatment by the heat treatment apparatus 1, titanium (Ti) or titaniumnitride (TiN) is deposited as a metal gate on the high dielectricconstant film 103.

The heat treatment apparatus 1 performs a heat treatment on thesemiconductor wafer W including the high dielectric constant film 103formed over the base material 101 with the silicon oxide film 102between the base material 101 and the high dielectric constant film 103.The procedure of the operation in the heat treatment apparatus 1 will bedescribed below. The procedure of the operation in the heat treatmentapparatus 1 proceeds as the controller 3 controls the respectiveoperating mechanisms of the heat treatment apparatus 1.

First, the semiconductor wafer W including the high dielectric constantfilm 103 deposited on the silicon oxide film 102 that is an interfacialfilm is transported into the chamber 6 of the heat treatment apparatus1. During the transport of the semiconductor wafer W into the chamber 6,the gate valve 185 is opened to open the transport opening 66. Then, atransport robot outside the heat treatment apparatus 1 transports thesemiconductor wafer W including the high dielectric constant film 103deposited thereover through the transport opening 66 into the heattreatment space 65 of the chamber 6. In the transport, air is carriedinto the heat treatment space 65 of the chamber 6 along with thetransport of the semiconductor wafer W into the heat treatment space 65because the pressure inside and outside the chamber 6 is equal toatmospheric pressure. To prevent this, nitrogen gas may be continuouslysupplied from the gas supply source 85 into the chamber 6 by opening thevalve 84 to cause the nitrogen gas to flow outwardly through the openedtransport opening 66, thereby minimizing the atmosphere outside theapparatus flowing into the chamber 6. It is preferable that the supplyflow rate of the nitrogen gas be higher when the gate valve 185 is openthan when the semiconductor wafer W is subjected to the heat treatment(e.g., if the supply flow rate is normally 30 liters per minute duringthe heat treatment, the supply flow rate is 120 liters per minute whenthe gate valve 185 is open). It is further preferable that the supplyflow rate of the nitrogen gas be increased, and at the same time, thevalve 89 be closed to stop exhausting the gas from the chamber 6. Thiscauses the nitrogen gas supplied into the chamber 6 to flow outwardlyonly through the transport opening 66, thereby effectively preventingoutside air from flowing into the chamber 6.

The semiconductor wafer W transported into the heat treatment space 65by the transport robot is moved forward to a position immediately overthe holder 7 and is stopped thereat. Then, the pair of transfer arms 11of the transfer mechanism 10 are moved horizontally from the retractedposition to the transfer operation position and are then moved upwardly,so that the lift pins 12 pass through the through holes 79 and protrudefrom the upper surface of the susceptor 74 to receive the semiconductorwafer W.

After the semiconductor wafer W is placed on the lift pins 12, thetransport robot moves out of the heat treatment space 65, and the gatevalve 185 closes the transport opening 66. Then, the pair of transferarms 11 move downwardly to transfer the semiconductor wafer W from thetransfer mechanism 10 to the susceptor 74 of the holder 7, so that thesemiconductor wafer W is held in a horizontal position. Thesemiconductor wafer W is held on the susceptor 74 in such a positionthat a front surface thereof over which the high dielectric constantfilm 103 is deposited is the upper surface. Also, the semiconductorwafer W is held inside the five guide pins 76 on the upper surface ofthe susceptor 74. The pair of transfer arms 11 moved downwardly belowthe susceptor 74 are moved back to the retracted position, that is, tothe inside of the recessed portion 62, by the horizontal movementmechanism 13.

After the semiconductor wafer W is housed in the chamber 6 and thetransport opening 66 is closed by the gate valve 185, the pressure inthe chamber 6 is reduced to a pressure lower than atmospheric pressure.Specifically, the transport opening 66 is closed, so that the heattreatment space 65 in the chamber 6 becomes an enclosed space. In thisstate, the valve 89 for exhausting the gas is opened while the valve 84for supplying the gas is closed. The controller 3 opens the exhaustvalve 192 provided in the bypass line 197 having the smallest pipediameter among the three bypass lines 197, 198, and 199 while operatingthe exhaust pump 191. The other exhaust valves 193 and 194 are closed.Thus, the gas is exhausted from the chamber 6 while no gas is suppliedinto the chamber 6, so that the pressure in the heat treatment space 65in the chamber 6 is reduced.

FIG. 10 is a graph showing changes in pressure in the chamber 6according to the first preferred embodiment. In FIG. 10, the horizontalaxis represents time, and the vertical axis represents pressure in thechamber 6. At the time when the semiconductor wafer W is housed in thechamber 6 and the transport opening 66 is closed, the pressure in thechamber 6 is equal to ordinary pressure Ps (=atmosphericpressure=approximately 101325 Pa). Then, at a time t1, a reduction inpressure in the chamber 6 starts. In an early stage of the pressurereduction, only the bypass line 197 having the smallest pipe diameteramong the three bypass lines 197, 198, and 199 is used, so that anexhaust flow rate is low and an exhaust speed is relatively low.

Then, at a time t2, the controller 3 opens all the three exhaust valves192, 193, and 194. As a result, the exhaust flow rate from the chamber 6increases, and the exhaust speed becomes faster. Then, at a time t3, thepressure (degree of vacuum) in the chamber 6 becomes equal to a pressureP1. The pressure P1 is, for example, approximately 100 Pa. That is,after the gas is exhausted at a low exhaust flow rate in the early stageof the pressure reduction, the exhaust flow rate is changed to a higherexhaust flow rate, and the gas is exhausted at the higher exhaust flowrate. The flow rate in the flow regulating valve 196 is constant in thefirst preferred embodiment.

If the gas is exhausted rapidly at a high exhaust flow rate from thestart of the pressure reduction, there is a danger that a large gas flowchange may occur in the chamber 6 to cause particles deposited onstructures (e.g., the lower chamber window 64) of the chamber 6 to swirlup and be deposited again on the semiconductor wafer W, resulting incontamination of the semiconductor wafer W. When the exhaust flow rateis changed to a higher exhaust flow rate and the gas is exhausted at thehigher exhausted flow rate after the gas is exhausted gently at a lowexhaust flow rate in the early stage of the pressure reduction, theswirling-up of particles in the chamber 6 is prevented.

When the exhaust part 190, which includes a detoxifying device (notshown) that renders the reactive gas such as ammonia harmless, exhauststhe gas at a high exhaust flow rate from the start of the pressurereduction, a large amount of gas may flow into the detoxifying device,so that the detoxifying device may become overloaded. The detoxifyingdevice can be prevented from becoming overloaded by exhausting the gasat a low exhaust flow rate in the early stage of the pressure reductionand then changing the exhaust flow rate to a higher exhaust flow rate toexhaust the gas, as in the present preferred embodiment. If the gas isexhausted at a high exhaust flow rate after the pressure in the chamber6 decreases to some extent, a relatively small amount of gas flows intothe exhaust part 190.

At the time t3 when the pressure in the chamber 6 becomes equal to thepressure P1, the valve 89 for exhausting the gas is closed and the valve84 for supplying the gas is opened, so that the gaseous mixture ofammonia and nitrogen gas that is a dilute gas is supplied into the heattreatment space 65 of the chamber 6. As a result, an ammonia atmosphereis provided around the semiconductor wafer W held by the holder 7 in thechamber 6. The concentration of ammonia in the ammonia atmosphere (i.g.,the mixing ratio of ammonia and nitrogen gas) is not particularlylimited and may be any value, which is, for example, not greater than 10vol % (in the present preferred embodiment, approximately 2.5 vol %).Also while the gaseous mixture of ammonia and nitrogen is supplied intothe chamber 6, only the bypass line 197 having the smallest pipediameter may be used to exhaust the gas from the chamber 6. In thiscase, needless to say, the supply flow rate of the gaseous mixture ishigher than the exhaust flow rate thereof.

By supplying the gaseous mixture into the chamber 6, the pressure in thechamber 6 is increased from the pressure P1 to return to the ordinarypressure Ps at a time t4. In the first preferred embodiment, thepressure in the chamber 6 is reduced once to the pressure P1 and thenreturned to the ordinary pressure Ps. This results in an oxygenconcentration of not greater than approximately 200 ppb in the ammoniaatmosphere in the chamber 6 after the pressure return to the ordinarypressure Ps.

After the time t4 when the pressure in the chamber 6 is returned to theordinary pressure Ps, the supply flow rate of the gaseous mixture ofammonia and nitrogen to the chamber 6 and the exhaust flow rate thereoffrom the chamber 6 are made equal to each other, so that the pressure inthe chamber 6 is maintained at the ordinary pressure Ps.

At the time t4 when the pressure in the chamber 6 is returned to theordinary pressure Ps, the 40 halogen lamps HL of the halogen heatingpart 4 turn on simultaneously to start preheating (or assist-heating)the semiconductor wafer W. The halogen light emitted from the halogenlamps HL is transmitted through the lower chamber window 64 and thesusceptor 74 that are made of quartz, and impinges upon the back surfaceof the semiconductor wafer W. The back surface of the semiconductorwafer W refers to a main surface thereof opposite to the front surfacewith the high dielectric constant film 103 deposited thereover. Thesemiconductor wafer W is irradiated with the halogen light from thehalogen lamps HL, so that the temperature of the semiconductor wafer Wincreases. It should be noted that the transfer arms 11 of the transfermechanism 10, which have been retracted to the inside of the recessedportion 62, do not block the heating using the halogen lamps HL.

The temperature of the semiconductor wafer W is measured with thecontact-type thermometer 130 when the halogen lamps HL perform thepreheating. Specifically, the contact-type thermometer 130 including abuilt-in thermocouple comes through the cut-out portion 77 into contactwith the lower surface of the semiconductor wafer W held by thesusceptor 74 to measure the temperature of the semiconductor wafer Wthat is during a temperature rise. The measured temperature of thesemiconductor wafer W is transmitted to the controller 3. The controller3 controls the output from the halogen lamps HL while monitoring whetherthe temperature of the semiconductor wafer W, which is during atemperature rise by the irradiation with light of the halogen lamps HL,reaches a predetermined preheating temperature T1. In other words, thecontroller 3 performs feedback control on the output of the halogenlamps HL, based on the value measured with the contact-type thermometer130, so that the temperature of the semiconductor wafer W is equal tothe preheating temperature T1. The preheating temperature T1 is in therange of 300° C. to 600° C., and is 450° C. in the present preferredembodiment. It should be noted that, when the temperature of thesemiconductor wafer W is increased by the irradiation with light fromthe halogen lamps HL, the temperature is not measured with the radiationthermometer 120. This is because the halogen light emitted from thehalogen lamps HL enters the radiation thermometer 120 in the form ofdisturbance light to obstruct the accurate measurement of thetemperature.

After the temperature of the semiconductor wafer W reaches thepreheating temperature T1, the controller 3 maintains the temperature ofthe semiconductor wafer W at the preheating temperature T1 for a shorttime. Specifically, at the time when the temperature of thesemiconductor wafer W measured with the contact-type thermometer 130reaches the preheating temperature T1, the controller 3 adjusts theoutput of the halogen lamps HL to maintain the temperature of thesemiconductor wafer W at approximately the preheating temperature T1.

Such preheating using the halogen lamps HL uniformly increases thetemperature of the entire semiconductor wafer W including the highdielectric constant film 103 to the preheating temperature T1. In thepreheating stage using the halogen lamps HL, the semiconductor wafer Wshows a tendency to be lower in temperature in a peripheral portionthereof where heat dissipation tends to occur than in a central portionthereof. However, the halogen lamps HL in the halogen heating part 4 aredisposed at a higher density in the region opposed to the peripheralportion of the semiconductor wafer W than in the region opposed to thecentral portion thereof. This causes a greater amount of light toimpinge upon the peripheral portion of the semiconductor wafer W whereheat dissipation tends to occur, thereby providing a uniform in-planetemperature distribution of the semiconductor wafer W in the preheatingstage. Further, the inner peripheral surface of the reflection ring 69mounted to the chamber side portion 61 is provided as a mirror surface.Thus, a greater amount of light is reflected from the inner peripheralsurface of the reflection ring 69 toward the peripheral portion of thesemiconductor wafer W. This leads to a more uniform in-plane temperaturedistribution of the semiconductor wafer W in the preheating stage. Itshould be noted that the pressure in the chamber 6 during the preheatingis maintained at the ordinary pressure Ps.

Then, the flash lamps FL emit a flash of light to perform a flashheating treatment at a time t5 when a predetermined time period haselapsed since the temperature of the semiconductor wafer W reached thepreheating temperature T1. At this time, part of the flash of lightemitted from the flash lamps FL travels directly toward the interior ofthe chamber 6. The remainder of the flash of light is reflected oncefrom the reflector 52, and then travels toward the interior of thechamber 6. The irradiation of the semiconductor wafer W with suchflashes of light achieves the flash heating treatment of thesemiconductor wafer W.

The flash heating treatment, which is achieved by the emission of aflash of light from the flash lamps FL, can increase the temperature ofthe front surface of the semiconductor wafer W in a short time.Specifically, the flash of light emitted from the flash lamps FL is anintense flash of light emitted for an extremely short period of timeranging from about 0.1 to 100 milliseconds as a result of the conversionof the electrostatic energy previously stored in the capacitor into suchan ultrashort light pulse. By irradiating the front surface of thesemiconductor wafer W, which includes the high dielectric constant film103 deposited over the base material 101 with the silicon oxide film 102between the base material 101 and the high dielectric constant film 103,with a flash of light from the flash lamps FL, the temperature of thefront surface of the semiconductor wafer W including the high dielectricconstant film 103 is momentarily increased to the treatment temperatureT2, so that the post deposition annealing is performed. The treatmenttemperature T2 that is a maximum temperature (peak temperature) reachedby the temperature of the front surface of the semiconductor wafer Wsubjected to irradiation with a flash of light is in the range of 600°C. to 1200° C., and is 1000° C. in the present preferred embodiment.

When the temperature of the front surface of the semiconductor wafer Wrises to the treatment temperature T2 in the ammonia atmosphere and thepost deposition annealing is performed, nitriding of the high dielectricconstant film 103 is accelerated, and defects such as point defectspresent in the high dielectric constant film 103 disappear. The lightemission time of the flash lamps FL is a short time period ranging fromapproximately 0.1 to 100 milliseconds. The time required for thetemperature of the front surface of the semiconductor wafer W toincrease from the preheating temperature T1 to the treatment temperatureT2 is also accordingly an extremely short time period of less than onesecond. After the flash irradiation, the temperature of the frontsurface of the semiconductor wafer W rapidly decreases from thetreatment temperature T2.

After the flash heating treatment, the valve 84 for supplying the gas isclosed to reduce the pressure in the chamber 6 again. The pattern of thepressure reduction at this time is identical to the pattern of thepressure reduction from the time t1 to the time t3 as described above.Specifically, in the early stage of the pressure reduction, only thebypass line 197 having the smallest pipe diameter among the three bypasslines 197, 198, and 199 is used, so that the exhaust flow rate isreduced to be relatively low. After that, all the three exhaust valves192, 193, and 194 are opened to increase the exhaust flow rate. That is,after the gas is exhausted at a low exhaust flow rate in the early stageof the pressure reduction, the exhaust flow rate is changed to a higherexhaust flow rate, and then the gas is exhausted at the higher exhaustflow rate. The reason why the exhaust flow rate is changed in two stagesto exhaust the gas as described is similar to the above.

Reducing the pressure in the chamber 6 to the pressure P1 again candischarge harmful ammonia from the heat treatment space 65 in thechamber 6. Subsequently, the valve 89 for exhausting the gas is closedand the valve 84 for supplying the gas is opened to supply a nitrogengas from the gas supply source 85 to the chamber 6, thereby returningthe pressure in the chamber 6 to the ordinary pressure Ps. At this time,the supply flow rate of the nitrogen gas is not less than 50 liters perminute. The halogen lamps HL also turn off, so that the temperature ofthe semiconductor wafer W also decreases from the preheating temperatureT1. The contact-type thermometer 130 or the radiation thermometer 120measures the temperature of the semiconductor waver W which is on thedecrease. The result of the measurement is transmitted to the controller3. The controller 3 monitors whether the temperature of thesemiconductor wafer W has decreased to a predetermined temperature,based on the result of the measurement.

After the temperature of the semiconductor wafer W decreases to thepredetermined temperature or below, the pair of transfer arms 11 of thetransfer mechanism 10 are moved horizontally again from the retractedposition to the transfer operation position and are then moved upwardly,so that the lift pins 12 protrude from the upper surface of thesusceptor 74 to receive the heat-treated semiconductor wafer W from thesusceptor 74. Subsequently, the transport opening 66 that has beenclosed by the gate valve 185 is opened, and the transport robot outsidethe heat treatment apparatus 1 transports the semiconductor wafer Wplaced on the lift pins 12 to the outside. Thus, the heat treatmentapparatus 1 completes the heating treatment of the semiconductor waferW.

In the first preferred embodiment, the pressure in the chamber 6 isreduced once to the pressure P1 lower than atmospheric pressure and thenreturned to the ordinary pressure Ps by supplying the gaseous mixture ofammonia and nitrogen. This results in an oxygen concentration of notgreater than approximately 200 ppb in the chamber 6 after the pressurereturn to the ordinary pressure Ps. If the atmosphere in the chamber 6is replaced with the gaseous mixture of ammonia and nitrogen while thepressure in the chamber 6 is not reduced but is maintained at ordinarypressure, the limit to which the oxygen concentration in the chamber 6can be decreased is approximately 2 ppm. That is, the process ofreducing the pressure in the chamber 6 once to the pressure P1 andthereafter returning the pressure in the chamber 6 to the ordinarypressure Ps as in the present preferred embodiment reduces the oxygenconcentration in the chamber 6 to approximately one-tenth of that in theprocess in which the pressure reduction is not performed.

As described above, since many defects such as point defects are presentin the high dielectric constant film 103 that has not undergone aspecific process after deposition, such defects need to be reduced bypost deposition annealing (PDA). In the presence of oxygen in the postdeposition annealing, the oxygen may be taken in to allow the siliconoxide film 102 underlying the high dielectric constant film 103 to grow,resulting in an increased film thickness. Consequently, a highdielectric constant cannot be achieved. Oxygen remaining in the chamber6 is a particular problem as a cause of such an increase in filmthickness. When the semiconductor wafer W is transported into thechamber 6 at ordinary pressure as in the present preferred embodiment, alarge amount of outside air is carried into the chamber 6 to increasethe residual oxygen concentration in the chamber 6. It is thuspreferable to minimize the oxygen concentration in the atmosphere duringthe post deposition annealing for the high dielectric constant film 103.In particular, the oxygen concentration is desirably not greater than 1ppm in the formation of a recent high dielectric constant gateinsulating film.

In the first preferred embodiment, the pressure in the chamber 6 isreduced once to the pressure P1 lower than atmospheric pressure and thenreturned to the ordinary pressure Ps, so that the oxygen concentrationin the heat treatment space 65 of the chamber 6 during the postdeposition annealing for the high dielectric constant film 103 isdecreased to approximately 200 ppb or less. This restricts an increasein thickness of the silicon oxide film 102 underlying the highdielectric constant film 103, which results from the oxygen taken infrom the heat treatment space 65 during the post deposition annealing.

The high dielectric constant film 103 immediately after depositioncontains oxygen, and thus, if the treatment time of the post depositionannealing becomes on the order of several seconds or more, the oxygenmay diffuse to increase the thickness of the silicon oxide film 102. Inthe first preferred embodiment, the front surface of the semiconductorwafer W is irradiated with a flash of light in the irradiation time ofless than one second from the flash lamps FL to raise the temperature ofthe front surface of the wafer in an extremely short time period, andthus, there is no time for oxygen to diffuse. This restricts an increasein thickness of the silicon oxide film 102 underlying the highdielectric constant film 103.

In the first preferred embodiment, the gaseous mixture of ammonia andnitrogen is introduced when the pressure in the chamber 6 is returned tothe ordinary pressure Ps, so that the front surface of the semiconductorwafer W is irradiated with a flash of light from the flash lamps FL inthe ammonia atmosphere to perform the post deposition annealing. Heatingthe high dielectric constant film 103 to the treatment temperature T2 inthe ammonia atmosphere causes nitriding of the high dielectric constantfilm 103 to proceed. This reduces the defects present in the highdielectric constant film 103 after the deposition, thus restricting aleakage current associated with these defects.

Performing the flash heating treatment in the ammonia atmospherenitrides the silicon oxide film 102 underlying the high dielectricconstant film 103. Nitriding of the silicon oxide film 102 moreeffectively restricts an increase in the thickness due to the oxidationof the silicon oxide film 102. Nitriding of the silicon oxide film 102slightly increases the dielectric constant of the silicon oxide film102. This restricts an increase in physical thickness of the siliconoxide film 102 and also reduces the electrical thickness thereof. Theflash irradiation time, which is an extremely short time of not greaterthan one second, restricts the diffusion of nitrogen to the channel sideeven when the silicon oxide film 102 is nitrided.

As described above, in pressure reduction in the chamber 6, the gas isexhausted at a low exhaust flow rate in the start of pressure reduction,and then, the exhaust flow rate is changed to a high exhaust flow rateto exhaust the gas. This prevents the particles from swirling up in thechamber 6 and also prevents the detoxifying device of the exhaust part190 from becoming overloaded.

Second Preferred Embodiment

A second preferred embodiment of the present invention will now bedescribed. The heat treatment apparatus 1 of the second preferredembodiment is identical in configuration to that of the first preferredembodiment. The procedure for treatment of a semiconductor wafer W inthe heat treatment apparatus 1 of the second preferred embodiment issubstantially identical to that of the first preferred embodiment. Thesecond preferred embodiment differs from the first preferred embodimentin the pressure to which the pressure in the chamber 6 is returned afterbeing decreased once.

FIG. 11 is a graph showing changes in pressure in the chamber 6according to the second preferred embodiment. In FIG. 11, the horizontalaxis represents time, and the vertical axis represents pressure in thechamber 6, as in FIG. 10. Indicated by the dotted lines in FIG. 11 is apressure change pattern obtained when the pressure in the chamber 6according to the first preferred embodiment is returned to the ordinarypressure Ps (the pattern of FIG. 10).

At the time when the semiconductor wafer W including the high dielectricconstant film 103 deposited thereover is housed in the chamber 6 and thetransport opening 66 is closed, the pressure in the chamber 6 is equalto the ordinary pressure Ps (=atmospheric pressure=approximately 101325Pa), as in the first preferred embodiment. Then, the reduction inpressure in the chamber 6 starts at the time t1. After the gas isexhausted at a low exhaust flow rate in the early stage of the pressurereduction, the exhaust flow rate is changed to a higher exhaust flowrate at the time t2, and the gas is exhausted at the higher exhaust flowrate, as in the first preferred embodiment. This prevents particles fromswirling up in the chamber 6 and also prevents the detoxifying devicefrom becoming overloaded.

At the time t3 when the pressure in the chamber 6 is equal to thepressure P1, the valve 89 for exhausting the gas is closed and the valve84 for supplying the gas is opened, so that the gaseous mixture ofammonia and nitrogen gas that is a diluent gas is supplied from the gassupply source 85 into the heat treatment space 65 of the chamber 6. Theoperation thus far described is similar to that of the first preferredembodiment. The pressure P1 is, for example, approximately 100 Pa.

In the second preferred embodiment, the pressure in the chamber 6 is notreturned to the ordinary pressure Ps but is returned to a pressure P2 ata time t6 by supplying the gaseous mixture. The pressure P2 is higherthan the pressure P1 and lower than the ordinary pressure Ps. Thepressure P2 is, for example, approximately 5000 Pa. Also in the secondpreferred embodiment, the pressure in the chamber 6 is reduced once tothe pressure P1 and then returned to the pressure P2 higher than thepressure P 1. This results in an oxygen concentration of not greaterthan approximately 200 ppb in the chamber 6 after the pressure return tothe pressure P2.

After the time t6 when the pressure in the chamber 6 is returned to thepressure P2, the supply flow rate of the gaseous mixture of ammonia andnitrogen to the chamber 6 and the exhaust flow rate thereof from thechamber 6 are made equal to each other, so that the pressure in thechamber 6 is maintained at the pressure P2. While the pressure in thechamber 6 is maintained at the pressure P2, the preheating of thesemiconductor wafer W is performed by the halogen lamps HL, and theflash heating treatment is thereafter performed at a time t7 byirradiating the front surface of the semiconductor wafer W with a flashof light from the flash lamps FL. The details of the preheating and theflash heating treatment in the second preferred embodiment are identicalto those in the first preferred embodiment. The temperature of the frontsurface of the semiconductor wafer rises to the treatment temperature T2by flash irradiation in the ammonia atmosphere, so that post depositionannealing for the high dielectric constant film 103 is performed.

After the flash heating treatment, the valve 84 for supplying the gas isclosed to reduce the pressure in the chamber 6 to the pressure P1 again,so that harmful ammonia is discharged from the heat treatment space 65of the chamber 6. Subsequently, the valve 89 for exhausting the gas isclosed and the valve 84 for supplying the gas is opened, so that thenitrogen gas is supplied from the gas supply source 85 into the chamber6 to return the pressure in the chamber 6 to the ordinary pressure Ps.The halogen lamps HL turn off. This causes the temperature of thesemiconductor wafer W to decrease from the preheating temperature T1.The procedure for the subsequent transport of the semiconductor wafer W,the temperature of which has been decreased to a predeterminedtemperature, out of the chamber 6 of the heat treatment apparatus 1 inthe second preferred embodiment is similar to that in the firstpreferred embodiment.

In the second preferred embodiment, the pressure in the chamber 6 isreduced once to the pressure P1 lower than atmospheric pressure and thenreturned to the pressure P2 by supplying the gaseous mixture of ammoniaand nitrogen into the chamber 6, resulting in an oxygen concentration ofnot greater than approximately 200 ppb in the heat treatment space 65 ofthe chamber 6 during the post deposition annealing for the highdielectric constant film 103, as in the first preferred embodiment. Thisrestricts an increase in thickness of the silicon oxide film 102underlying the high dielectric constant film 103 due to the oxygen takenin from the heat treatment space 65 during the post depositionannealing.

As in the first preferred embodiment, the temperature of the frontsurface of the semiconductor wafer W is increased to the treatmenttemperature T2 in an extremely short time by irradiating the frontsurface of the semiconductor wafer W with a flash of light from theflash lamps FL for an irradiation time period of less than one second.This results in an extremely short treatment time for the postdeposition annealing and does not allow time for oxygen to diffuse.Thus, an increase in thickness of the silicon oxide film 102 underlyingthe high dielectric constant film 103 is restricted.

In the second preferred embodiment, the post deposition annealing isperformed on the high dielectric constant film 103 by irradiating thefront surface of the wafer W with a flash of light, with the pressure inthe chamber 6 maintained at the pressure p2 lower than ordinarypressure, that is, under an increased pressure. Under a reducedpressure, the density of gas molecules is small, resulting in a longermean free path. When the post deposition annealing is performed on thehigh dielectric constant film 103 under a reduced pressure, accordingly,the mean free path of ammonia is increased, resulting in a uniformreaction of ammonia and the high dielectric constant film 103 to theheat treatment. Needless to say, when the post deposition annealing isperformed on the high dielectric constant film 103 under a reducedpressure, the partial pressure itself of ammonia is reduced remarkablycompared with the case in which the treatment is performed at ordinarypressure as in the first preferred embodiment. For this reason,nitriding of the high dielectric constant film 103 proceeds further whenthe post deposition annealing is performed on the high dielectricconstant film 103 at ordinary pressure as in the first preferredembodiment.

Performing the post deposition annealing on the high dielectric constantfilm 103 under a reduced pressure promotes the desorption of impurities,for example, carbon (C), contained in the high dielectric constant film103 after the deposition. By discharging such desorbed impurity elementsfrom the chamber 6, the impurities are prevented from being depositedagain on and contaminating the front surface of the semiconductor waferW. This prevents the degradation in device performance and a decrease inyield.

Also, the temperature rise efficiency is enhanced during the preheatingand during the flash heating treatment because the absorption of halogenlamp light and flashes of light by an atmosphere gas in the chamber 6 isreduced. This also increases the attained surface temperature of thesemiconductor wafer W during the flash heating treatment.

Performing the heating treatment on the semiconductor wafer W under areduced pressure reduces the influence of convection in the chamber 6 toimprove the uniformity of the in-plane temperature distribution of thesemiconductor wafer W.

In the second preferred embodiment, the pressure in the chamber 6 is notreturned to the ordinary pressure Ps but is returned from the pressureP1 to the pressure

P2 lower than atmospheric pressure. The time required for the pressurereturn is made shorter by the return of the pressure in the chamber 6 tothe pressure P2 as in the second preferred embodiment than by the returnof the pressure in the chamber 6 to the ordinary pressure Ps as in thefirst preferred embodiment. The timing of the flash irradiation may bemoved forward by the amount of the reduction in the time required forthe pressure return (as shown in FIG. 11, the time t7 of the flashirradiation in the second preferred embodiment is earlier than the timet5 of the flash irradiation in the first preferred embodiment). As aresult, the return of the pressure in the chamber 6 to the pressure P2lower than atmospheric pressure as in the second preferred embodimentimproves the throughput in the heat treatment apparatus 1.

Third Preferred Embodiment

A third preferred embodiment of the present invention will now bedescribed. The heat treatment apparatus 1 of the third preferredembodiment is exactly identical in configuration to that of the firstpreferred embodiment. The procedure for treatment of the semiconductorwafer W in the heat treatment apparatus 1 of the third preferredembodiment is substantially similar to that of the first preferredembodiment. The third preferred embodiment differs from the firstpreferred embodiment in pressure changes in the chamber 6.

FIG. 12 is a graph showing changes in pressure in the chamber 6according to the third preferred embodiment. In FIG. 12, the horizontalaxis represents time, and the vertical axis represents pressure in thechamber 6, as in FIG. 10.

At the time when the semiconductor wafer W including the high dielectricconstant film 103 deposited thereover is housed in the chamber 6 and thetransport opening 66 is closed, the pressure in the chamber 6 is equalto the ordinary pressure Ps (=atmospheric pressure=approximately 101325Pa), as in the first preferred embodiment.

Then, the reduction in pressure in the chamber 6 starts at the time t1.In the third preferred embodiment, the exhaust flow rate in the threebypass lines 197, 198, and 199 is made constant, and the exhaust flowrate from the chamber 6 is continuously increased with time by means ofthe flow regulating valve 196. That is, the exhausting of the gas startsat a relatively low exhaust flow rate in the early stage of the pressurereduction, and the exhaust flow rate is increased graduallycontinuously. This prevents particles from swirling up in the chamber 6and also prevents the detoxifying device from becoming overloaded, as inthe first preferred embodiment. Also, increasing the exhaust flow ratein a continuous and stepless manner prevents particles from swirling updue to abrupt changes in exhaust flow rate.

At the time t3 when the pressure in the chamber 6 is equal to thepressure P1, the valve 89 for exhausting the gas is closed and the valve84 for supplying the gas is opened, so that the gaseous mixture ofammonia and nitrogen gas that is a diluted gas is supplied from the gassupply source 85 into the heat treatment space 65 of the chamber 6 toreturn the pressure in the chamber 6. The pressure P1 is, for example,approximately 100 Pa.

In the third preferred embodiment, the supply flow rate of the treatmentgas to the chamber 6 is continuously increased with time by means of theflow regulating valve 90. That is, the supply of the gas starts at arelatively low supply flow rate in the early stage of the pressurereturn, and the supply flow rate is increased gradually continuously. Ifthe gas is supplied rapidly at a high supply flow rate from the start ofthe pressure return, there is a danger that particles deposited on thestructures of the chamber 6 may swirl up, as in the case of the pressurereduction. When the supply of the gas starts at a relatively low supplyflow rate in the early stage of the pressure return and the supply flowrate is increased gradually, such particles in the chamber 6 areprevented from swirling up. Also, increasing the supply flow rate in acontinuous and stepless manner prevents particles from swirling up dueto abrupt changes in supply flow rate.

In the third preferred embodiment, the pressure in the chamber 6 isreturned to a pressure P3 exceeding the ordinary pressure Ps at a timet8 by supplying the gaseous mixture into the chamber 6. The pressure P3is higher than atmospheric pressure and is, for example, approximately0.15 MPa. Also in the third preferred embodiment, the pressure in thechamber 6 is reduced once to the pressure P1 and then returned to thepressure P3 higher than the pressure P1. This results in an oxygenconcentration of not greater than approximately 200 ppb in the chamber 6after the pressure return to the pressure P3.

After the time t8 when the pressure in the chamber 6 is returned to thepressure P3, the supply flow rate of the gaseous mixture of ammonia andnitrogen to the chamber 6 and the exhaust flow rate thereof from thechamber 6 are made equal to each other, so that the pressure in thechamber 6 is maintained at the pressure P3. While the pressure in thechamber 6 is maintained at the pressure P3, the preheating of thesemiconductor wafer W is performed by the halogen lamps HL, and theflash heating treatment is thereafter performed at a time t9 byirradiating the front surface of the semiconductor wafer W with a flashof light from the flash lamps FL. The details of the preheating and theflash heating treatment in the third preferred embodiment are identicalto those in the first preferred embodiment. By irradiating the frontsurface of the semiconductor wafer W with a flash of light in theammonia atmosphere, the post deposition annealing on the high dielectricconstant film 103 is performed.

After the flash heating treatment, the valve 84 for supplying the gas isclosed to reduce the pressure in the chamber 6 to the pressure P1 again,so that harmful ammonia is discharged from the heat treatment space 65of the chamber 6. Also at this time, the exhaust flow rate from thechamber 6 is continuously increased with time by means of the flowregulating valve 196, thus preventing the particles from swirling up dueto the gas exhaustion.

Subsequently, the valve 89 for exhausting the gas is closed and thevalve 84 for supplying the gas is opened to supply the nitrogen gas intothe chamber 6 from the gas supply source 85, thereby returning thepressure in the chamber 6 to the ordinary pressure Ps. The supply flowrate of the treatment gas to the chamber 6 is continuously increasedwith time by means of the flow regulating valve 90, thus preventing theparticles from swirling up due to the gas exhaustion.

The halogen lamps HL turn off, so that the temperature of thesemiconductor wafer W decreases from the preheating temperature T1. Theprocedure for the subsequent transport of the semiconductor wafer W, thetemperature of which has been decreased to a predetermined temperature,out of the chamber 6 of the heat treatment apparatus 1 in the thirdpreferred embodiment is similar to that in the first preferredembodiment.

Factors responsible for the particles swirling up in the chamber 6include the flash irradiation in addition to the gas supplied to andexhausted from the chamber 6. In the flash irradiation from the flashlamps FL, the temperature of the front surface of the semiconductorwafer W is momentarily increased, whereas the temperature of the backsurface of the semiconductor wafer W is not increased so much from thepreheating temperature T1. Thus, a large temperature difference arisesbetween the front and back surfaces of the semiconductor wafer W. Thiscauses the thermal expansion of only the front surface of thesemiconductor wafer W, resulting in an abrupt deformation of thesemiconductor wafer W. As a result, the semiconductor wafer W vibrateson the susceptor 74 to create particles, which in turn swirl up in thechamber 6.

To effectively discharge such particles resulting from the flashirradiation from the chamber 6, the third preferred embodiment performsthe following operation. Also when ammonia is discharged after the flashheating treatment and then the nitrogen gas is supplied into the chamber6 to return the pressure in the chamber 6 to the ordinary pressure Ps,the nitrogen gas is caused to flow at a flow rate in the range of 50 to100 liters per minute in the chamber 6, thereby sweeping away theparticles resulting from the flash irradiation. This prevents theparticles resulting from the flash irradiation from being deposited onand contaminating the semiconductor wafer W.

When the nitrogen gas is supplied into the chamber 6 to return thepressure in the chamber 6 to the ordinary pressure Ps after ammonia isdischarged, the valve 84 for supplying the gas may also be opened tosupply the nitrogen gas into the chamber 6 while the valve 89 forexhausting the gas is left open. This enables more effective dischargeof the particles resulting from the flash irradiation from the chamber6.

In the third preferred embodiment, the pressure in the chamber 6 isreduced once to the pressure P1 lower than atmospheric pressure and thenreturned to the pressure P3 by supplying the gaseous mixture of ammoniaand nitrogen into the chamber 6, resulting in an oxygen concentration ofnot greater than approximately 200 ppb in the heat treatment space 65 ofthe chamber 6 during the post deposition treatment of the highdielectric constant film 103, as in the first preferred embodiment. Thisrestricts an increase in thickness of the silicon oxide film 102underlying the high dielectric constant film 103 resulting from theoxygen taken in from the heat treatment space 65 during the postdeposition annealing.

In the third preferred embodiment, the front surface of thesemiconductor wafer W is irradiated with a flash of light in theirradiation time of less than one second from the flash lamps FL toraise the temperature of the front surface of the wafer in an extremelyshort time, as in the first preferred embodiment. Thus, the treatmenttime of the post deposition annealing is extremely short, and there isno time for oxygen to diffuse, thus restricting an increase in thicknessof the silicon oxide film 102 underlying the high dielectric constantfilm 103.

In the third preferred embodiment, the post deposition annealing isperformed on the high dielectric constant film 103 by irradiating thefront surface of the semiconductor wafer W with a flash of light, withthe pressure in the chamber 6 maintained at the pressure P3 higher thanatmospheric pressure, that is, under an increased pressure. The partialpressure of ammonia is also high under the increased pressure, thuspromoting nitriding even at a temperature lower than the treatmenttemperature T2 according to the first preferred embodiment. In otherwords, the treatment temperature during flash irradiation is lowered.

In the third preferred embodiment, the exhaust flow rate and the supplyflow rate are changed in a stepless and continuous manner during thepressure reduction and the pressure return in the chamber 6. Thisprevents particles from swirling up due to abrupt changes in suppliedand exhausted gas.

Fourth Preferred Embodiment

A fourth preferred embodiment of the present invention will now bedescribed. The heat treatment apparatus 1 of the fourth preferredembodiment is exactly identical in configuration with that of the firstpreferred embodiment. The procedure for treatment of the semiconductorwafer W in the heat treatment apparatus 1 of the fourth preferredembodiment is substantially similar to that of the first preferredembodiment. The fourth preferred embodiment differs from the firstpreferred embodiment in atmosphere control during the heat treatment ofa semiconductor wafer W.

While both of the preheating and flash heating treatment of asemiconductor wafer W are performed in an ammonia atmosphere in thefirst preferred embodiment, in the fourth preferred embodiment, a supplyof ammonia is stopped during the flash heating treatment. Specifically,as in the first preferred embodiment, a semiconductor wafer W includingthe high dielectric constant film 103 deposited thereover is housed inthe chamber 6. Subsequently, the pressure in the chamber 6 is reducedonce to the pressure P1, and then, a gaseous mixture of ammonia andnitrogen gas that is a diluted gas is supplied into the heat treatmentspace 65 of the chamber 6 to return the pressure in the heat treatmentspace 65 to the ordinary pressure Ps.

After the pressure in the chamber 6 is returned to the ordinary pressurePs, 40 halogen lamps HL of the halogen heating part 4 turn on, so thatpreheating of the semiconductor wafer W starts. In this preheatingstage, a gaseous mixture of ammonia and nitrogen is supplied to thechamber 6, and also, the gas is exhausted from the chamber 6, thusmaintaining the pressure in the chamber 6 at the ordinary pressure Ps.That is, in the preheating step, a gaseous mixture of ammonia andnitrogen is supplied into the chamber 6 to provide an ammoniaatmosphere. Preheating is performed to raise the temperature of asemiconductor wafer W to the preheating temperature T1 in the ammoniaatmosphere, thus nitriding the high dielectric constant film 103 to someextent.

In the fourth preferred embodiment, then, the supply of ammonia into thechamber 6 is stopped before irradiation of light from the flash lampsFL. In stopping a supply of ammonia, a supply of a nitrogen gas may beincreased at a flow rate corresponding to the reduced supply flow rateof ammonia, or an exhaust flow rate of the nitrogen gas may be reduced.In any case, the pressure in the chamber 6 is maintained at the ordinarypressure Ps also after the supply of ammonia is stopped.

Stopping a supply of ammonia while continuously exhausting the gas fromthe chamber 6 reduces the concentration of ammonia in the chamber 6.Then, the flash lamps FL emit a flash of flight to perform a flashheating treatment at the time when the concentration of ammonia in thechamber 6 is not greater than one-tenth of the concentration obtainedbefore a supply of ammonia is stopped. For this light emission control,a densitometer to measure the atmospheric concentration of ammonia maybe placed in the chamber 6. Alternatively, a time required for theconcentration of ammonia to be not greater than one-tenth of theoriginal concentration may be determined in advance, for example, byexperiment to perform flash irradiation at the time after the determinedtime has elapsed since a supply of ammonia was stopped.

The semiconductor wafer W is irradiated with a flash of light while asupply of ammonia to the chamber 6 is stopped, thus restrictingnitriding of the high dielectric constant film 103 and also enables thehydrogen, which has entered the high dielectric constant film 103 by thereaction of ammonia and the high dielectric constant film 103 in thepreheating step, to be desorbed.

The procedure after the flash heating treatment is performed as in thefirst preferred embodiment. Specifically, after the flash heatingtreatment, the pressure in the chamber 6 is reduced to the pressure P1again, and then, a nitrogen gas is supplied into the chamber 6 to returnthe pressure in the chamber 6 to the ordinary pressure Ps. Also, thehalogen lamps HL turn off, and the semiconductor wafer W, thetemperature of which has decreased to a predetermined temperature, istransported out of the chamber 6 of the heat treatment apparatus 1.

In the fourth preferred embodiment, ammonia is supplied into the chamber6 in the preheating step, and also, the supply of ammonia into thechamber 6 is stopped during the flash irradiation. This enables the highdielectric constant film 103 to be nitrided to some extent and alsoenables the hydrogen that has entered the high dielectric constant film103 to be desorbed.

Modifications

While the preferred embodiments of the present invention have beendescribed above, various modifications to the present invention inaddition to those described above may be made without departing from thescope and spirit of the invention. For example, the pressure P1 that isthe pressure to be attained during the pressure reduction in the chamber6 is approximately 100 Pa in the preferred embodiments above, but is notlimited to this value. The pressure P1 may take any appropriate value.To reduce the oxygen concentration to be attained in the chamber 6 toapproximately one-tenth, it is sufficient that the pressure P1 that isthe pressure to be attained during the pressure reduction in the chamber6 is approximately one-tenth (approximately 10000 Pa) of atmosphericpressure. Making the pressure P1 lower (i.e., reducing the pressure to ahigher vacuum) achieves a lower concentration of oxygen remaining in thechamber 6 after the pressure return, but requires a longer time toreduce the pressure to the pressure P1. It is therefore preferable thatthe pressure P1 be set in consideration of a balance between the oxygenconcentration required for the execution of the post depositionannealing and the throughput.

It is preferable that the pressure P1 that is the pressure to beattained during the pressure reduction in the chamber 6 be set to be notgreater than one-hundredth of the pressure in the chamber 6 during theheat treatment of the semiconductor wafer W, that is, a target pressure(the ordinary pressure Ps in the first preferred embodiment, thepressure P2 in the second preferred embodiment, the pressure P3 in thethird preferred embodiment) during the return of pressure in the chamber6. This reduces the influence of remaining air on an ammonia atmosphereduring the heat treatment of the semiconductor wafer W.

While the three bypass lines 197, 198, and 199 are provided to controlthe exhaust flow rate from the chamber 6 in the preferred embodimentsabove, the number of bypass lines may be not less than two. The exhaustflow rate from the chamber 6 may be controlled by a throttle valve or agas ballast provided in place of the plurality of bypass lines 197, 198,and 199. Alternatively, a mass flow controller may be used in place ofthe flow regulating valves 90 and 196.

The exhaust flow rate from the chamber 6 during the pressure reductionis changed in two levels in the first and second preferred embodiments,and the exhaust flow rate is increased in a stepless and continuousmanner in the third preferred embodiment. The present invention,however, is not limited to the above, and for example, the exhaust flowrate may be changed in multiple levels. That is, it is only necessarythat the exhaust flow rate during the reduction in pressure in thechamber 6 be increased with time.

Similarly, while the supply flow rate to the chamber 6 during thepressure return is increased in a stepless and continuous manner in thethird preferred embodiment, it may be changed in two or more levels toincrease the supply flow rate. That is, it is only necessary that thesupply flow rate during the return of pressure in the chamber 6 beincreased with time.

In the reduction and return of the pressure in the chamber 6, thecontroller 3 may control the valves and the like based on the amount ofelapsed time from the start (time t1) of the pressure reduction or mayfeedback-control the valves and the like based on the result of themeasurement of the pressure in the heat treatment space 65 by means ofthe pressure gauge 180. In the control based on the elapsed time, arelationship between the elapsed time and the pressure in the chamber 6may be determined by experiment or simulation.

While the gaseous mixture of ammonia and nitrogen gas is supplied intothe chamber 6 in the preferred embodiments above, the present inventionis not limited to this and can use, for example, hydrogen gas (H₂),argon (Ar), helium (He), or xenon (Xe) as a diluted gas to be mixed withammonia. A gaseous mixture of ammonia and any of the above-mentionedgases can be supplied into the heat treatment space 65 to provide anammonia atmosphere in the chamber 6. In particular, helium has highcapability of extracting heat and is used also as a cooling gas. The useof a gaseous mixture of ammonia and helium accordingly increases thespeed of cooling a semiconductor wafer W after the flash heatingtreatment.

The treatment gas may be an oxygen-based reactive gas such as a nitrogenoxide, oxygen, or ozone. For example, a trace amount of ozone may beintroduced for heat treatment of a high dielectric constant film. Insuch a case, the controllability of the concentration of anoxygen-containing gas such as ozone will decrease unless theconcentration of oxygen, which is a background, remaining in the chamber6 is reduced sufficiently. The controllability of the concentration ofan oxygen-based gas can be enhanced by reducing the concentration ofoxygen in the heat treatment space 65 of the chamber 6 in advance, as inthe preferred embodiments above. Therefore, the technology according tothe present invention becomes significant even when an oxygen-basedreactive gas is used.

In the fourth preferred embodiment, the reduction in pressure in thechamber 6 may be started simultaneously with stopping a supply ofammonia. In this case, the semiconductor wafer W is preheated in anammonia atmosphere at ordinary pressure, and a flash heating treatmentis performed while reducing a pressure in the chamber 6.

In the preferred embodiments above, a heat treatment is performed on thesemiconductor wafer W including the high dielectric constant film 103,serving as a gate insulating film, deposited on the silicon oxide film102 that serves as an interfacial film (FIG. 9). Alternatively, a heattreatment may be performed on the semiconductor wafer

W including a metal gate further deposited on the high dielectricconstant film 103. The raw material for the metal gate may be, forexample, titanium nitride (TiN), titanium aluminum (TiAl), or tungsten(W). Preheating and flash heating treatment are performed on thesemiconductor wafer W including the metal gate deposited on the highdielectric constant film 103 in a procedure similar to those of thepreferred embodiments. As a result, post deposition annealing can beperformed to eliminate a large number of defects present in the highdielectric constant film 103 after the deposition.

In the case where a heat treatment is performed on the semiconductorwafer W including the metal gate formed thereover, the metal gate itselfmay be oxidized. In some cases, oxygen may diffuse through the metalgate and the high dielectric constant film 103 to increase the thicknessof the silicon oxide film 102. As in the preferred embodiments above, byreducing the pressure in the chamber 6 once to the pressure P1 and thenreturning the pressure, the concentration of oxygen in the chamber 6 isset to be extremely low, and then, preheating and flash heatingtreatment are performed on the semiconductor wafer W. This restricts anincrease in thickness of the silicon oxide film 102 and also preventsoxidation of the metal gate itself.

The material for the base material 101 is not limited to silicon and maybe germanium (Ge) or silicon germanium. When the material for the basematerial 101 is not silicon, the material for the interfacial filmunderlying the high dielectric constant film 103 may not be silicondioxide.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

What is claimed is:
 1. A method of irradiating a substrate including ahigh dielectric constant film deposited thereover with a flash of lightto heat said substrate, the method comprising: (a) transporting asubstrate including a high dielectric constant film deposited thereoverinto a chamber; (b) reducing a pressure in said chamber to a firstpressure lower than atmospheric pressure; (c) returning the pressure insaid chamber from the first pressure to a second pressure higher thanthe first pressure; and (d) irradiating a front surface of saidsubstrate with a flash of light from a flash lamp while maintaining thepressure in said chamber at the second pressure.
 2. The method accordingto claim 1, wherein a reactive gas containing ammonia is introduced intosaid chamber in said step (c).
 3. The method according to claim 2,wherein the first pressure is not greater than one-hundredth of thesecond pressure.
 4. The method according to claim 2, further comprising(e) before said step (d), raising a temperature of said substrate to apredetermined preheating temperature, wherein a supply of the reactivegas into said chamber is performed in said step (e), and the supply ofthe reactive gas into said chamber is stopped after said step (d). 5.The method according to claim 4, wherein the supply of the reactive gasis stopped, and simultaneously, the reducing the pressure in saidchamber is started.
 6. The method according to claim 1, wherein thesecond pressure is higher than the first pressure and lower thanatmospheric pressure.
 7. The method according to claim 1, wherein thesecond pressure comprises atmospheric pressure.
 8. The method accordingto claim 1, wherein the second pressure is higher than atmosphericpressure.
 9. The method according to claim 1, wherein an exhaust flowrate from said chamber is increased with time in said step (b).
 10. Themethod according to claim 1, wherein a supply flow rate into saidchamber is increased with time in said step (c).
 11. The methodaccording to claim 1, wherein after said step (d), when a gas in saidchamber is discharged and then an inert gas is supplied into saidchamber so that the pressure in said chamber returns to atmosphericpressure, the inert gas is caused to flow at a flow rate ranging from 50to 100 liters per minute in said chamber.
 12. A heat treatment apparatusfor irradiating a substrate including a high dielectric constant filmdeposited thereover with a flash of light to heat said substrate, theapparatus comprising: a chamber that houses said substrate; a flash lampthat irradiates said substrate housed in said chamber with a flash oflight; an exhaust part that exhausts an atmosphere in said chamber; agas supply part that supplies a predetermined treatment gas to saidchamber; and a controller that controls said exhaust part and said gassupply part so that a front surface of said substrate is irradiated witha flash of light from said flash lamp while a pressure in said chamberis reduced to a first pressure lower than atmospheric pressure and thenreturned to a second pressure higher than the first pressure.
 13. Theheat treatment apparatus according to claim 12, wherein said gas supplypart supplies a reactive gas containing ammonia into said chamber whenthe pressure in said chamber is returned from the first pressure to thesecond pressure.
 14. The heat treatment apparatus according to claim 13,wherein the first pressure is not greater than one-hundredth of thesecond pressure.
 15. The heat treatment apparatus according to claim 13,further comprising a preheating part that raises a temperature of saidsubstrate to a predetermined preheating temperature before saidsubstrate is irradiated with the flash of light, wherein said controllercontrols said exhaust part and said gas supply part so that the reactivegas is supplied into said chamber when said preheating part preheatssaid substrate and that the supply of the reactive gas into said chamberis stopped after said substrate is irradiated with the flash of light.16. The heat treatment apparatus according to claim 15, wherein saidcontroller controls said exhaust part and said gas supply part to stopthe supply of the reactive gas and simultaneously start reducing thepressure in said chamber.
 17. The heat treatment apparatus according toclaim 12, wherein the second pressure is higher than the first pressureand lower than atmospheric pressure.
 18. The heat treatment apparatusaccording to claim 12, wherein the second pressure comprises atmosphericpressure.
 19. The heat treatment apparatus according to claim 12,wherein the second pressure is higher than atmospheric pressure.
 20. Theheat treatment apparatus according to claim 12, wherein said controllercontrols said exhaust part so that an exhaust flow rate from saidchamber increases with time when the pressure in said chamber is reducedto the first pressure.
 21. The heat treatment apparatus according toclaim 12, wherein said controller controls said gas supply part so thata supply flow rate to said chamber increases with time when the pressurein said chamber is returned from the first pressure to the secondpressure.
 22. The heat treatment apparatus according to claim 12,wherein said controller controls said exhaust part and said gas supplypart so that, after the irradiation with the flash of light, when a gasin said chamber is discharged and then an inert gas is supplied intosaid chamber to return the pressure in said chamber to atmosphericpressure, the inert gas is caused to flow in said chamber at a flow rateranging from 50 to 100 liters per minute.